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Laboratory Experiments on Three-Dimensional Seepage Erosion Undercutting of Vegetated Banks. R. Cancienne, M. Chu-Agor, and G. A. Fox. Riparian Vegetation. OKLAHOMA STATE UNIVERSITY Biosystems & Agricultural Engineering Department. Stabilizing Effects Increased soil cohesion from roots

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laboratory experiments on three dimensional seepage erosion undercutting of vegetated banks

Laboratory Experiments on Three-Dimensional Seepage Erosion Undercutting of Vegetated Banks

R. Cancienne, M. Chu-Agor, and G. A. Fox

riparian vegetation
Riparian Vegetation

OKLAHOMA STATE UNIVERSITY

Biosystems & Agricultural Engineering Department

  • Stabilizing Effects
    • Increased soil cohesion from roots
    • Precipitation interception via canopy
  • Destabilizing Effects
    • Increased infiltration due to

macropore formation along

roots

    • Greater surcharge from

plant mass

Riparian vegetation on Rio Nigua, Puerto Rico; www.pr.nrcs.usda.gov

objective
Objective

OKLAHOMA STATE UNIVERSITY

Biosystems & Agricultural Engineering Department

Analyze the effects of vegetation and root reinforcement on seepage erosion and undercutting.

slide4

OKLAHOMA STATE UNIVERSITY

Biosystems & Agricultural Engineering Department

Vegetated Soil Block Experiments

  • Simulation Constraints
    • Loamy sand
    • α= 90o
    • ρb = 1.6 g cm-3
    • H = 25 cm
  • Experiments: 3 vegetated and 1 unvegetated soil block
  • Used 3D scanner to collect seepage images
vegetated soil block experiments
Vegetated Soil Block Experiments

OKLAHOMA STATE UNIVERSITY

Biosystems & Agricultural Engineering Department

Growing period: (November to January)

Vegetation 1

Vegetation 2

Vegetation 3

Control

vegetated soil block experiments1
Vegetated Soil Block Experiments

OKLAHOMA STATE UNIVERSITY

Biosystems & Agricultural Engineering Department

  • Loamy sand
  • α= 90o
  • ρb = 1.6 g cm-3
  • H = 25 cm
  • Switchgrass: 2 months old
vegetated soil block experiments2
Vegetated Soil Block Experiments

Root Cohesion: Wu et al. (1979):

OKLAHOMA STATE UNIVERSITY

Biosystems & Agricultural Engineering Department

  • Root Area Ratio, Ar/A
  • Ar=root area; A=Area of failure plane

(b) Root tensile strength. Tr

Measuring length and diameter of roots on the failure plane

Universal Testing Machine

slide8

OKLAHOMA STATE UNIVERSITY

Biosystems & Agricultural Engineering Department

Results

vegetated soil block experiments3
Vegetated Soil Block Experiments

Root tensile strength

OKLAHOMA STATE UNIVERSITY

Biosystems & Agricultural Engineering Department

vegetated soil block experiments4
Vegetated Soil Block Experiments

Wu et al. (CGJ, 1979):

Field cr values for switchgrass = 18 kPa

(Simon and Collison, ESPL 2002)

OKLAHOMA STATE UNIVERSITY

Biosystems & Agricultural Engineering Department

vegetated soil block experiments5
Vegetated Soil Block Experiments

Effects of root reinforcement on time to failure

OKLAHOMA STATE UNIVERSITY

Biosystems & Agricultural Engineering Department

slide12

OKLAHOMA STATE UNIVERSITY

Biosystems & Agricultural Engineering Department

Vegetated Soil Block Experiments

  • Shape different from unvegetated, unweathered soil block.

Unvegetated bank (Chu-Agor et al, 2008)

Vegetated bank

vegetated soil block experiments6
Vegetated Soil Block Experiments

Shape of undercut dependent on root presence

OKLAHOMA STATE UNIVERSITY

Biosystems & Agricultural Engineering Department

(a)

(b)

conclusions
Conclusions

Laboratory cr values less than field values

Seepage erosion patterns differed with unvegetated soil block experiments

Additional experiment during active growing stage of switchgrass

OKLAHOMA STATE UNIVERSITY

Biosystems & Agricultural Engineering Department

slide15

OKLAHOMA STATE UNIVERSITY

Biosystems & Agricultural Engineering Department

Vegetated Soil Block Experiments

Previously …..

This time…

20 clusters, March to May

10 clusters, November to January

slide16

OKLAHOMA STATE UNIVERSITY

Biosystems & Agricultural Engineering Department

Vegetated Soil Block Experiments

Root puller

slide17

Thank you!

Questions?